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Visualizing pair formation on the atomic scale in the high-Tc superconductor Bi2Sr2CaCu2O8+delta
Kenjiro K Gomes1, Abhay N Pasupathy, Aakash Pushp
1Department of Physics, Joseph Henry Laboratories, Princeton University, Princeton, New Jersey 08544, USA.
Nature
|June 1, 2007
Summary
In high-temperature superconductors, electron pairing gaps form in nanoscale regions above the critical temperature (Tc). These localized pairing phenomena provide a microscopic basis for understanding fluctuating superconductivity.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Superconductivity
Background:
- Conventional superconductors exhibit electron pairing at the superconducting transition temperature (Tc), forming an energy gap (Delta).
- High-Tc superconductors display a partial gap in their electronic density of states (DOS) above Tc, raising questions about its association with pairing.
Purpose of the Study:
- To investigate the spatial and temperature-dependent formation of pairing gaps in high-Tc superconductors.
- To determine the relationship between gap formation and the temperature at which incoherent pairs form.
Main Methods:
- Spatially resolved measurements using scanning tunnelling microscopy (STM).
- Analysis of Bi2Sr2CaCu2O8+delta samples with varying critical temperatures (Tc) and hole concentrations (0.12 to 0.22).
Main Results:
- Pairing gaps nucleate in nanoscale regions above Tc for doping levels from 0.16 to 0.22.
- These nanoscopic pairing regions proliferate with decreasing temperature, leading to a distribution of gap sizes.
- Every pairing gap locally develops at a characteristic temperature Tp, following 2Delta/k(B)Tp = 7.9 ± 0.5.
- At low doping (<0.14), distinct DOS changes suggest a phenomenon competing with electron pairing.
Conclusions:
- The study reveals the first direct, spatially resolved evidence of nanometre-sized pairing regions in high-Tc superconductors above Tc.
- These findings offer a microscopic explanation for previously observed fluctuating superconducting responses above Tc in similar materials.
- The results highlight the complex interplay of pairing and other electronic phenomena in high-Tc superconductors.
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